1. Field of the Invention
This invention relates to optical data recording devices utilizing rotating disc recording media, and more particularly but not by way of limitation, to a recording device having a holographic grating for beam splitting a laser light source.
2. Brief Description of the Prior Art
Heretofore, in many optical storage devices a polarized beam splitter is used as an optical switch. The splitter passes all of the light from a laser light source to a recording medium, and at the same time it isolates the reflected beam from the medium to prevent the light from returning to the laser. This phenomenon is based on the principle that a specially coated beam splitter can reflect most of the light which is polarized perpendicular to its plane of incidence and transmit all the light polarized in its plane of incidence. The use of polarized beam splitters with quarter wave retardation plates is expensive.
In U.S. Pat. Nos. 4,542,492, 4,513,408, 4,489,408, 3,422,273, 4,025,949, 3,978,278 and 3,924,063, various types of optical storage devices are described. None of these prior art patents specifically describes or uses a holographic grating for transmitting and reflecting a laser light source used in optical recording.